Nail drivers have long been known in the prior art. An early form thereof is shown in U.S. Pat. No. 913,014 issued Feb. 23, 1909 to Kafer; this comprises an axially extended tube, a ram mounted for reciprocal movement in the tube, a handle for the ram and a nail holder formed as a coaxial extension of the tube. Little problem has been experienced in the past when using such tool for stapling or nailing wood or similar material. However, it is not believed that there have been any successful commercial embodiments of this type of tool that are suitable for driving nails into hard substrates as is now desired.
Much of the commercial activity in this area has been concentrated on powder actuated tools. These may be of a a high velocity type or a low velocity type; both types have contributed to many industrial accidents. Manual nail drivers may not be mis-used in the same way as the powder actuated tools as the velocity, and hence the energy, of a nail which may be freely expelled from such tools is extremely low.
Part of the problem in relation to the use of manual tools for driving nails into hard substances resides in the limited impact forces that can be generated, particularly when operated under adverse conditions. It is generally found that when the impact force does not exceed what appears to be a critical minimum limit, spalling of the concrete takes place, and that even though completely set the nail is not retained with as much force as when it is set using adequate impact force.
There are several constraints in manufacturing a manual nail driving tool of the type referred to. Thus the tool must be of robust design so as to withstand the rough handling that it is likely to receive on a construction site. The tool must be priced so as to be competitive with other alternative nail setting tools. These factors do not permit a highly engineered tool considering the tool in more detail, the tube portion thereof may typically have a length of some 18-24 inches and an internal diameter of about 1 inch. The ram of the tool is similarly dimensioned and must be pushed the length of the tube in order to generate the maximum impact force. It will be appreciated that particularly under adverse conditions, such as when the nail driver is operated other than in a vertical position, there may be a relatively large area of a surface contact between the tube and ram, and that high frictional losses may ensue to reduce the available impact force. Also the end of the ram is normally equipped with a pin as an integral extension thereof, the pin entering the nail holder and contacting the nail to be driven. The nail holder normally has a bore opening therethrough only nominally greater than the diameter of the pin, and serves to concentre the pin so as to strike a nail held therein squarely. The impact force of the ram may also be partially expended by the pin striking the walls of the bore opening.
It is object of my invention to provide a manual nail driver suitable for use in driving nails into hard substrates.
It is a further object of my invention to provide in such nail driver improved structure so as to limit the above defects and maximize the impact forces, whilst at the same time providing an economic construction.